Kit for a Chimney Through a Garage

The diameter is measured on the inside of the (inner) pipe. Common sizes are 4", 6", and 8", depending on your appliance. A 4" liner is typically used for gas appliances and some pellet stoves. Most wood stoves use a 6" internal outlet, while larger stoves or open fireplaces may need 8". Check your appliance manual or look at the round collar where the flue connects.

What type of ceiling does the chimney pass through in the living room?

Select your ceiling type. We’ll choose the correct support box automatically:

• Flat ceiling → we use an 11" Ceiling Support Box.
• Flat ceiling - extra thick → we use a 24" Ceiling Support Box (trimmed to the roof pitch). Select this if your ceiling structure is thicker than 9" (joists + drywall + framing), so the box can extend 2" below the ceiling.
• Sloped ceiling (vaulted/cathedral) up to 8/12 pitch → we use a 24" Ceiling Support Box (trimmed to the roof pitch).
• Sloped ceiling (vaulted/cathedral) steeper than 8/12 → we use a 36" Ceiling Support Box (trimmed to the roof pitch).

This kit also includes an Attic Insulation Shield and the complete roof exit parts (roof flashing + storm collar + cap). A Floor/Ceiling Radiation Shield is not required for this kit (only used in multi-story homes).

 

 

 

 

 

 

 

 

More info (technical): how box height is chosen

Installers can size the support box by the joist depth and the desired drop below the finished ceiling (so the black stovepipe connector can attach and clearances are met).

Joist Depth*	Desired Drop Below Ceiling	Recommended Box Height
6–8 inches	2–4 inches	12" box
10–12 inches	4–6 inches	24" box
12–14+ inches	6–10 inches	36" box

* For sloped ceilings, the support box must extend fully through the ceiling and be trimmed to the roof pitch so it sits flush. Always maintain the required 2" clearance to combustibles.

 

 

 

 

 

 

 

 

Use a ceiling support box when your chimney pipe passes vertically through a ceiling and into the attic or upper floor. It ensures structural support, safe clearance, and code compliance. For the area's of use also see below.

 

Our Square Ceiling Support Box for 6" chimney measures 12.2" x 12.2" and 14.3" x 14.3" for 8" chimney.  Both support boxes should fit between the rafters with room to spare so your mark does not need to be perfectly centered between the rafters but it does need to be centered enough for the support box to fit.

Determine the Height of the Stove pipes

Take a measurement from the ceiling to the floor.

Now subtract the total height of the stove (measured from the bottom of the stove to the top of the flue collar) from the ceiling height.  Don't forget to subtract any hearth or hearth pad that the stove will sit on.

You also need to subtract the distance that the ceiling support box will extend down into the home. The support box must extend a minimum of 2" below the ceiling to meet clearances.

You only need to be close with your measurements here, not exact. Our black stove pipes cannot be cut to size so you will need one of our telescoping lengths to complete your installation. This gives you lots of "play" in your measurement.

Height of the Class A Pipes

That is : 

Distance from the attic floor to the roof 

              + 

Height on the roof

 

Calculate the required height on the roof

The termination of a chimney above a roof must comply with NFPA 211 and/or CAN/CSA-A405. These codes require the chimney to terminate at least 3 feet above the highest point where it passes through the roof, and 2 feet higher than any part of any building within 10 feet. A UL- or ULC-listed chimney cap must be installed.

What is the 3-2-10 Rule for Chimney Height?

If your chimney is too short, it won't draft properly. Smoke may enter your living space instead of venting outside. But if the chimney is too tall, the flue gases can cool excessively, reducing draft and potentially creating backdraft.

To avoid these problems, use the 3-2-10 rule:

• The chimney must be at least 3 feet higher than the highest point where it passes through the roof.
• It must also be 2 feet taller than any part of any building within a 10-foot radius.

This ensures a safe and effective draft, even with sloped or pitched roofs.

How to Calculate the Correct Chimney Height

Knowing your roof pitch helps determine how high the chimney must extend. Roof pitch is the vertical rise per 12 inches of horizontal run. For example, a 7/12 pitch means the roof rises 7 inches for every 12 inches of run.

Step-by-Step Calculation:

1. Measure Roof Pitch: Identify the pitch (e.g., 7/12).

2. Measure Horizontal Distance from Ridge: Use the actual distance or 10 feet (whichever applies).

3. Calculate Height: Multiply pitch rise by horizontal distance, then add 24 inches.

Example 1: Chimney More Than 10 Feet from Ridge

• Pitch: 7/12

• Distance: 10 feet

• Height: 7 x 10 = 70 inches

• Final chimney height = 70 + 24 = 94 inches above roof

Example 2: Chimney 4 Feet from Ridge

• Pitch: 7/12

• Distance: 4 feet

• Height: 7 x 4 = 28 inches

• Final chimney height = 28 + 24 = 52 inches above roof

Why Proper Clearance Matters

The 3-2-10 rule isn’t just about smoke control. It helps prevent fire risks by keeping hot embers away from the roof and ensures compliance with building codes. Always double-check your local building codes before installation, and consult a professional if in doubt.

• A Roof Flashing provides leak prevention for the roof penetration of the chimney system.
• Storm Collar works together with the roof flashing to provide a waterproof seal where the chimney passes through the roof.

The type of flashing depends on the pitch of the roof.

For more information see our Blog

 

Determine the Free-Standing Chimney Length

 

Measure from the highest support point—normally the top wall bracket or roof flashing—to the top of the chimney.

 

• Up to 5 feet: no Extended Roof Brace is required.
• More than 5 feet and up to 10 feet: one Extended Roof Brace is required.
• The chimney must not extend more than 10 feet above its highest support point.

 

If the unsupported length would exceed 10 feet, contact us before ordering. This wizard does not calculate such installations.